title: Lock-in amplification for implantable multiwavelength pulse oximeters.
abstract: Standard as well as multiwavelength pulse oximetry as established methods for measuring blood oxygen saturation or fractions of dyshemoglobins suffer from different kinds of interference and noise. Employing lock-in technique as a read-out approach for multiwavelength pulse oximetry is proposed here and strongly decreases such signal disturbance. An analog lock-in amplifier was designed to modulate multiple LEDs simultaneously and to separate the signals detected by a single photodiode. In vivo measurements show an improved signal-to-noise ratio of photoplethysmographic signals and a suppression of interference by means of the lock-in approach. This allows the detection of higher order overtones and, therefore, more detailed data for pulse wave analysis, especially for implantable sensors directly applied at arteries.
authors.forename: Michael
authors.initials: M
authors.lastname: Theodor
authors.forename: Utku
authors.initials: U
authors.lastname: Karakas
authors.forename: Dominic
authors.initials: D
authors.lastname: Ruh
authors.forename: Hans
authors.initials: H
authors.lastname: Zappe
authors.forename: Andreas
authors.initials: A
authors.lastname: Seifert
mesh_terms: D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D020007:Implants, Experimental; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D010092:Oximetry / Q000295:instrumentation*; D010100:Oxygen / Q000097:blood; D063177:Pulse Wave Analysis; D059629:Signal-To-Noise Ratio
chemical_list: D006454:Hemoglobins; C015185:dyshemoglobins; D010100:Oxygen